While driving on a family trip in Chiba, Kogoro's car breaks down. They stop by a house, where Kogoro, Ran, and Conan meet the famous lawyer Kensuke Tachibana and his secretary Yuuichi Sakuraba, and later they meet his caretaker Yaeko Kamei, his wife Yuki Tachibana, and his office's accountant Noriko Sugimura and lawyer Fumio Fujisawa. Tachibana is getting threatening letters from a man with the initials "T.K." The next morning, the dog Yohan is acting strangely. Tachibana leaves the house for a fishing trip, while Kogoro, Ran, and Conan walk the dog. It reacts wildly when it sees a suspicious person in a red hat, on a boat. Later that day, Tachibana's boat is found, halfway sinking, and his body is found deep in the ocean.

Murder

Location:

Chiba Bay

Victim:

Kensuke Tachibana

Age:

62 years old

Cause of death:

Drowning

Suspects:

Tatsuya Kumada

A local detective and his assistant arrive at the scene, and the man with the initials "T.K." is found out to be Tatsuya Kumada, an old client of the lawyer, and becomes the number one criminal. However, when they go to his apartment, they find him dead, seemingly hanging himself in a suicide.

Suicide?

Location:

Kumada apartment

Victim:

Tatsuya Kumada

Cause of death:

Hanging

However, the clues say otherwise. Could someone have killed both the lawyer and the client?

Conan discovers that, five years before, a man was killed in a "perfect crime" by the man who had killed himself, with the initials "T.K."

Murder (Past)

Location:

Tsuruta apartment

Victim:

Masahiko Tsuruta

Cause of death:

Hanging

Suspects:

Tatsuya Kumada

Conan uses this clue, as well as other clues via help from an old boat rental owner, to deduce how the lawyer was killed. He then visits the old home where the man who was killed five years before lived, and gets information from an old lady there, and discovers a dog house sign that says "Johann". Conan had finally figured it out who the real murderer is.

Conan deduces who the murderer of both men is, and knocks out Kogoro with his stun gun wristwatch to solve the case, trying to get the murderer to admit themselves that they had done it. First, Yuuichi Sakuraba says that Kensuke Tachibana is threatening him, and he couldn't take it anymore. But then Kogoro via Conan reveals the real culprit to be Yaeko Kamei, but she admit that she killed Kensuke and Tatsuya. First, she put sleeping pills in Kensuke's water bottle, then after they had left, she disguised as Kumada and left through the back door and used a boat to go to Tachibana's boat. Afterwards, Tachibana's boat capsized with them. Later that evening, Yaeko went shopping and parked her car in the parking lot, then she immediately disguised somewhere and took a train to Kumada's apartment, then shows a nameplate in Masahiko Tsuruta's yard and the name was Johann and reveals in German, it would be "Yohan". Yohan is Yaeko's pet dog and Johann was probably the name her son who graduated in Germany, gave and reveals her real name as Tamiko Tsuruta and reveals as Masahiko Tsuruta's mother, who was murdered by Tatsuya Kumada and says that yesterday at the cape, Yohan was chasing after the boat she was on, even she was disguised, Yohan recognized her.

Tamiko confesses and reveals her second son Katsuhiko Tsuruta died last year and says Yohan is her only family and says that she lied, saying he was a stray dog, and they started living in Tachibana's villa and reveals she fought many times at court, but no one noticed her, the court's decision was unfair and grew old because of that and then half a year ago, Kumada finally appeared and she overheard the washing machine trick. In jail, Kumada said he would pay any amount of money, even though Tachibana knew that Kumada murdered Masahiko, he acquitted Kumada of the crime for money. That day, she followed Kumada to his apartment with his hat that he left, she thought of this crime and Kogoro via Conan reveals the threat that looked like they were from Kumada, Yaeko was sending them to Tachibana. And Yaeko says: "Since yesterday, I have been so scared, I'm finally relieved."

The next morning, when they drive home with the repaired car, Kogoro, Ran, and Conan have another breakdown. Kogoro stops desperately, while Ran and Conan enjoy the sea view.

The character designs and surnnames for policemen Baba and Inoki are the same of the real-life Japanese professional wrestlers Giant Baba, died about two years before the original airdate, and Antonio Inoki.

Kyoko Tachibana, the PSB freelance lawyer in Zero the Enforcer, bears a resemblance with Kensuke Tachibana and has the same surname kanji. The movie doesn't show the picture on her former law office's desk, but the painting near the door is about the threes on the left of Tachibana villa, and the one behind her about some threes at the cape where he lived. Open spoiler box to see images.